[File under "obscure macrology" and "macro-expansion performance".]
The `identifier-prune-lexical-context' function added in 4.2.0.2 strips lexical information from an identifier if the information doesn't affect the identifier's binding (or, more generally, the binding of identifiers derived from a given list of symbols). There's also a derived `quote-syntax/prune' form, which is like `quote-syntax' on an identifier, but that prunes the lexical information from the identifier. Note that `(quote-syntax/prune id)' is different from `(identifier-prune-lexical-context (quote-syntax id))'; the later would wait until the expression is evaluated to prune lexical information, while the former prunes it as the expression is expanded (so that the lexical information isn't kept in bytecode, etc.). You might wonder why irrelevant lexical information would be preserved in the first place. The reason is `datum->syntax': The macro system doesn't know whether lexical information will be transferred to some other datum, where that extra information could become relevant. Probably `datum->syntax' is too powerful an operation, but I don't know how to get rid of it. So, we've fought the excessive-information problem with a lot of encoding, caching, and lazy-initialization tricks. These tricks, however, fail for nested internal-definition contexts created by `package', especially when `define*'s are used within a package to create layers of bindings. I couldn't find new tricks that work well enough without a pruning hint from the programmer. Use `quote-syntax/prune' or `identifier-prune-lexical-context' to potentially reduce bytecode size when an identifier's context won't be transferred to other syntax objects --- or perhaps only to '#%top, which `quote-syntax/prune' excludes from pruning in addition to the identifier's symbol. Pruning probably is not worthwhile on a macro template, but it can be useful in the expansion of forms like `define-struct' and `package' that keep lists of identifiers. _________________________________________________ For list-related administrative tasks: http://list.cs.brown.edu/mailman/listinfo/plt-dev
